Method to etch non-volatile metal materials

ABSTRACT

A method for etching a stack with at least one metal layer in one or more cycles is provided. An initiation step is preformed, transforming part of the at least one metal layer into metal oxide, metal halide, or lattice damaged metallic sites. A reactive step is performed providing one or more cycles, where each cycle comprises providing an organic solvent vapor to form a solvated metal, metal halide, or metal oxide state and providing an organic ligand solvent to form volatile organometallic compounds.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority under 35 USC§120 to co-pending U.S. patent application Ser. No. 14/325,911 filed onJul. 8, 2014, entitled “Method to Etch Non-Volatile Metal Materials”which claims priority under 35 U.S.C. §119(e) to U.S. Provisional PatentApplication No. 61/971,032, filed on Mar. 27, 2014, entitled “Methods toEtch and to Remove Post Etch Metallic Residue” all of which are herebyincorporated by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates to etching a layer of non volatilematerials through a mask during the production of a semiconductordevice. More specifically, the present invention relates to etching ametal layers.

During semiconductor wafer processing, features may be etched through ametal layer. In the formation of magnetoresistive random-access memory(MRAM) or resistive random-access memory (RRAM) devices, a plurality ofthin metal layers or films may be sequentially etched. For MRAM aplurality of thin metal layers may be used to form metal tunnelingjunction stacks.

Patterning non-volatile metal materials such as MRAM in a traditionalreactive ion etcher (RIE) is challenging due to low volatility of theetch byproducts. The non-volatile sidewall passivation could cause thedevice short across the magnetic tunneling junction area and degradationof electric performance. Ion Beam Etching (IBE) has been used for MRAMpatterning to clean the sidewall and maintain the material integrity.However, IBE is limited by the aspect ratio (<2:1) for advancedtechnology nodes with high pattern density.

SUMMARY OF THE INVENTION

To achieve the foregoing and in accordance with the purpose of thepresent disclosure, a method of etching a stack with at least one metallayer in one or more cycles is provided. An initiation step ispreformed, transforming part of the at least one metal layer into metaloxide, metal halide, or lattice damaged metallic sites. A reactive stepis performed providing one or more cycles, where each cycle comprisesproviding an organic solvent vapor to form a solvated metal, metalhalide, or metal oxide state and providing an organic ligand solvent toform volatile organometallic compounds.

In another manifestation, a method of etching a stack with at least onemetal layer in one or more cycles is provided. An initiation step ispreformed, transforming part of the at least one metal layer into metaloxide, metal halide, or lattice damaged metallic sites. A reactive stepis performed providing an organic solvent vapor to form a solvatedmetal, metal halide, or metal oxide state or providing an organic ligandsolvent to form volatile organometallic compounds.

In another manifestation, a method of etching a stack with at least onemetal layer in one or more cycles is provided. An initiation step ispreformed, transforming part of the at least one metal layer into metaloxide, metal halide, or lattice damaged metallic sites. A reactive stepis performed providing an organic solvent vapor to form a solvatedmetal, metal halide, or metal oxide state.

In another manifestation, a method of etching a stack with at least onemetal layer in one or more cycles is provided. An initiation step ispreformed, transforming part of the at least one metal layer into metaloxide, metal halide, or lattice damaged metallic sites. A reactive stepis performed providing an organic ligand solvent to form volatileorganometallic compounds.

These and other features of the present invention will be described inmore detail below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a high level flow chart of an embodiment of the invention.

FIGS. 2A-H are schematic views of a stack processed according to anembodiment of the invention.

FIG. 3 is a schematic view of an etch reactor that may be used foretching.

FIG. 4 illustrates a computer system, which is suitable for implementinga controller used in embodiments of the present invention.

FIG. 5 is a more detailed flow chart of the reactive step.

FIGS. 6A-E are schematic views of a MRAM stack processed according to anembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

To facilitate understanding, FIG. 1 is a high level flow chart of aprocess used in an embodiment of the invention. A substrate with a stackwith at least one metal containing layer is provided (step 104). Aninitiation step is provided (step 108). A reactive step is provided(step 112). A desorption step is provided (step 116).

EXAMPLES

In an example of a preferred embodiment of the invention, a substratewith a stack with at least one metal layer is provided (step 104). FIG.2A is a cross-sectional view of a stack 200 over a substrate 204. Thestack 200 comprises at least one metal layer 208 disposed below a mask212. The at least one metal layer 208 may comprise one or more metallayers with non-metal layers. In addition, one or more layers may bedisposed between the substrate 204 and the at least one metal layer 208.In addition, one or more layers may be disposed between the at least onemetal layer 208 and the mask 212. In this example the at least one metallayer 208 is a tantalum as bottom electrode layer under a platinummanganese (PtMn), or CoPt/CoPd layer, which is a fixed magnetic layer inMRAM film stack.

In one embodiment, all processing may be performed in a single plasmaetch chamber. FIG. 3 is a schematic view of an etch reactor that may beused in practicing such an embodiment. In one or more embodiments of theinvention, an etch reactor 300 comprises a gas distribution plate 306providing a gas inlet and a chuck 308, within an etch chamber 349,enclosed by a chamber wall 350. Within the etch chamber 349, a substrate204 on which the stack is formed is positioned on top of the chuck 308.The chuck 308 may provide a bias from the ESC source 348 as anelectrostatic chuck (ESC) for holding the substrate 304 or may useanother chucking force to hold the substrate 204. A heat source 310,such as heat lamps, is provided to heat the metal layer. An ion source324, a solvent vaporizer 326, and a ligand vaporizer 328 are connectedto the etch chamber 349 through the distribution plate 306. A ligandsource 327 is connected to the ligand vaporizer 328. A solvent source325 is connected to the solvent vaporizer 326. An ESC temperaturecontroller is connected to the chuck 308, and provides temperaturecontrol of the chuck 308.

FIG. 4 is a high level block diagram showing a computer system 400,which is suitable for implementing a controller 335 used in embodimentsof the present invention. The computer system may have many physicalforms ranging from an integrated circuit, a printed circuit board, and asmall handheld device up to a huge super computer. The computer system400 includes one or more processors 402, and further can include anelectronic display device 404 (for displaying graphics, text, and otherdata), a main memory 406 (e.g., random access memory (RAM)), storagedevice 408 (e.g., hard disk drive), removable storage device 410 (e.g.,optical disk drive), user interface devices 412 (e.g., keyboards, touchscreens, keypads, mice or other pointing devices, etc.), and acommunication interface 414 (e.g., wireless network interface). Thecommunication interface 414 allows software and data to be transferredbetween the computer system 400 and external devices via a link. Thesystem may also include a communications infrastructure 416 (e.g., acommunications bus, cross-over bar, or network) to which theaforementioned devices/modules are connected.

Information transferred via communications interface 414 may be in theform of signals such as electronic, electromagnetic, optical, or othersignals capable of being received by communications interface 414, via acommunication link that carries signals and may be implemented usingwire or cable, fiber optics, a phone line, a cellular phone link, aradio frequency link, and/or other communication channels. With such acommunications interface, it is contemplated that the one or moreprocessors 402 might receive information from a network, or might outputinformation to the network in the course of performing theabove-described method steps. Furthermore, method embodiments of thepresent invention may execute solely upon the processors or may executeover a network such as the Internet in conjunction with remoteprocessors that shares a portion of the processing.

The term “non-transient computer readable medium” is used generally torefer to media such as main memory, secondary memory, removable storage,and storage devices, such as hard disks, flash memory, disk drivememory, CD-ROM and other forms of persistent memory and shall not beconstrued to cover transitory subject matter, such as carrier waves orsignals. Examples of computer code include machine code, such asproduced by a compiler, and files containing higher level code that areexecuted by a computer using an interpreter. Computer readable media mayalso be computer code transmitted by a computer data signal embodied ina carrier wave and representing a sequence of instructions that areexecutable by a processor.

An initiation step is provided (step 108). The initiation step initiatesreactive sites transforming part of the at least one metal layer intometal oxide, metal halide, or lattice damaged metallic sites. In thisembodiment, the initiation step is provided by using an ionic flux orion beam to covert part of the at least one metal layer 208 into a metaloxide, metal halide, or lattice damaged metallic sites. In this example,an oxygen plasma or ion beams through IBE can be applied to the wafersurface to oxidize the film not covered by the mask. In another example,a chlorine plasma or low energy inert gas plasma ion can also beapplied. FIG. 2B is a cross-sectional view of the stack 200 after theinitiation step has been provide (step 108). Unmasked surface layers ofthe at least one metal layer 208 are exposed to the ionic flux or ionbeam and transformed into modified metallic sites 216. In this example,the modified metallic sites 216 are metal transformed into metal oxide,metal halide, or lattice damaged metallic sites. In this example, ionsare provided from the ion source 324 into the etch chamber 349.

A reaction step is provided (step 112). FIG. 5 is a more detailed flowchart of providing a reaction step (step 112), which is provided in anembodiment of the invention. In this embodiment, the reaction step (step112) comprises a solvate modified metallic sites step (step 504) and aligand complex formation step (step 508). In this embodiment, thesolvate modified metallic sites step (step 504) forms solvated metal atthe modified metallic sites. In this embodiment, the modified metallicsites are exposed to a vapor solvent. A solvent source 325 providessolvent to the solvent vaporizer 326, which vaporizes the solvent andprovides the solvent vapor into the etch chamber 349. Such solvents maybe alcohols, amine, or hydrocarbons. Such solvents may be polar ornon-polar, base or acidic. Providing a solvated metal is helpful inlocalizing the metal electron and facilitating the organic ligandattachment. In this embodiment, the ligand complex formation step (step508) provides ligand vapor which transform the solvated metal intoorganometallic compounds. A ligand source 327, provides ligands to theligand vaporizer 328, which vaporizes the ligands and provides theligand vapor to the etch chamber 349. In this example, the ligand vaporprovides organic ligands. The organic ligands that may be used to formligand complexes may include acetylacetonate (acac) family (such asbis(acac)-EDIM), acetic acid, amides, amidinates (tBuNC(R)Net), allyls,ethylene, acetylene, and cyclo-pentadienyl. In this embodiment, thesolvate modified metallic sites step (step 504) and a ligand complexformation step (step 508) are performed cyclically a plurality of times.In other embodiments, the solvate modified metallic sites step and aligand complex formation step may be performed simultaneously. Wherethese steps are performed simultaneously, the ligand concentration mustby high. FIG. 2C is a cross-sectional view of the stack 200 after thereactive step has been provide (step 112). The modified metallic siteshave been transformed into organometallic sites 220. In this embodiment,the ESC temperature controller 350, may be used to cool the chuck 308.In addition, the heat source 310 may be off, so that the stack 200 iskept cooler to increase the deposition of the vapors.

A desorption step is provided (step 116). In this embodiment, theorganometallic sites 220 are heated causing the desorption oforganometallic material. The heating may be achieved by heating a chuckholding the substrate 204 or by radiation directly heating theorganometallic sites 220. In this example, the heat source 310 may useradiant heat to directly the organometallic sites 220. The ESCtemperature controller 350 may be used to heat the chuck 308, whichheats the stack 200. FIG. 2D is a cross-sectional view of the stack 200after the desorption step has been provide (step 116). Theorganometallic sites have been removed by desorption, leaving partiallyetched sites 224.

The desorption step can also be realized with fine controlled ion energysputtering so the organometallic compounds are detached but the ligandsare not detached from metal sites.

Since the at least one metal layer 208 is only partially etched, thecycle is continued (step 120), which returns to the initiation step(step 108). The same initiation step as described above may be used orthe parameters may be changed. FIG. 2E is a cross-sectional view of thestack 200 after the initiation step has been provide (step 108).Unmasked surface layers of the at least one metal layer 208 is exposedto the ionic flux or ion beam and transformed into modified metallicsites 228.

A reaction step is provided (step 112). The same reaction step asdescribed above may be used or parameters may be changed. FIG. 2F is across-sectional view of the stack 200 after the reactive step has beenprovide (step 112). The modified metallic sites have been transformedinto organometallic sites 232.

A desorption step is provided (step 116). In this embodiment, theorganometallic sites 232 are heated causing the desorption oforganometallic material. The same desorption step as described above maybe used or parameters may be changed. FIG. 2G is a cross-sectional viewof the stack 200 after the desorption step has been provide (step 116).The organometallic sites have been removed by desorption, leavingpartially etched sites 224.

The cycle is continued (step 120) until the etch process is completed.FIG. 2H is a cross-sectional view of the stack 200 after the etching ofthe at least one metal layer 208 is completed.

This embodiment provides a plasma free etching processes. Otherembodiments may use a plasma during the initiation step or thedesorption step. Such a plasma may be a downstream plasma provided tothe etch chamber 349 from a plasma source or may be created in situ,wherein the etch chamber 349 would require a precursor gas source and aplasma excitation system. In other embodiments an ion flux of O₂, COS,or CH₃OH may be used to provide the initiation step. In otherembodiments a vapor generated from H₂O₂, HClO, O₃, SOCl₂, NH₄OH, HCHO,or CH₃COOH may be used to provide the initiation step. In otherembodiments, a catalyst may be used during the reaction step to increasethe reaction rate.

FIG. 6A is a schematic cross-sectional view of a stack 600 used inanother embodiment of the invention. In this stack 600 an inter layerdielectric layer (ILD) 604 is placed over a substrate, not shown. Abottom electrode 608 is formed over the ILD 604. In this embodiment, thebottom electrode 608 is formed from Ta, Ti, or W. In other embodiments,other similar metals may be used for the bottom electrode 608. A bottomnon-volatile metal (NVM) (pinned layer) layer 612 is formed over thebottom electrode 608. In this embodiment, the bottom NVM layer is formedfrom MnPt, CoPt, CoPd, or CoFe. In other embodiments, other similaralloys may be used for the bottom NVM layer 612. A tunneling layer 616of magnesium oxide (MgO) is formed over the bottom NVM layer 612. A topNVM layer 620 is formed over the tunneling layer 616. In thisembodiment, the top NVM layer 620 is formed from CoFe, CoFeB, Ru, CoPt,or CoPd. In other embodiments the top NVM layer 620 is formed of othermetals or alloys. In this embodiment, the combination of the bottom NVMlayer 612, the tunneling layer 616, and the top NVM layer 620 forms amagnetic tunnel junction (MTJ). A patterned hardmask 624 is formed overthe top NVM layer 620. In this embodiment the patterned hardmask 624 isTa, TaN, TiN or W, and is used as an electrode. In other embodiments,other electrode materials may be used.

In this embodiment, the top NVM layer 620 and tunneling layer 616 areetched using an RIE or IBE, which in this embodiment etches 2-3 nm ofthe bottom NVM 612. An IBE etch is able to etch the top NVM layer 620and tunneling layer 616 without forming sidewall deposition and withoutdamaging the tunneling layer 616. FIG. 6B is a schematic cross-sectionalview of the stack after the NVM layer 620 and tunneling 616 have beenetched. Using IBE to only etch the top NVM layer 620 and tunneling layer616 lowers the IBE sidewall angle/aspect ratio limitation whilemaintaining tunneling layer 616 integrity without deposition build up.

An oxide or nitride spacer is formed around the partially etched stack600. FIG. 6C is a schematic cross-sectional view of the stack 600 afterthe spacer 628 has been formed. The spacer seals the tunneling layer 616during subsequent etching. The spacer thickness is approximately 2 to 5nm. RIE or IBE sputtering is used to open the spacer 628. FIG. 6D is aschematic cross-sectional view of the stack 600 after the spacer 628have been opened.

The stack is then subjected to an etch process, as shown in FIG. 1,wherein the patterned hard mask 624, the top NVM layer 620, thetunneling layer 616, and the spacer 628 provide a patterned mask foretching the bottom NVM layer 612. In this example, the initiation step(step 108) is provided by providing an oxidation by providing a pressureof 4 to 80 mTorr. 50 to 500 sccm of O₂ and 0 to 500 sccm Ar are flowedinto the etch chamber 349. 200 to 1500 TCP power at 13 MHz is providedto form the gas into a plasma. A bias voltage from 20 to 500 volts isprovided. The oxidation process is maintained for 5 to 60 seconds. In analternative embodiment, the initiation step may be provided bychlorination. In such a process a pressure of 4 to 80 mTorr is provided.50 to 500 sccm of Cl₂ and 0 to 500 sccm of Ar is flowed into the etchchamber 349. 200 to 1500 TCP power at 13 MHz is provided to form the gasinto a plasma. A bias voltage from 20 to 500 volts is provided. Thechlorination process is maintained for 5 to 60 seconds.

In this example, the solvate modified metallic sites step (step 504) isprovided by providing a vapor of an organic acid. The ligand complexformation step (step 508) is provided by providing a vapor of a ligand.A pressure of 20 mTorr to 1 Torr is provided during the solvation andligand complex formation steps with or without a carrier gas, wherethese steps may be cycled multiple times to enhance the reaction.

In this example the desorption step (step 116) is provided by providinga light plasma sputtering. In one example, the light plasma sputteringmay be accomplished by providing 4 to 80 mTorr of chamber pressure. 50to 500 sccm Ar is flowed into the etch chamber 349. 200 to 1500 TCPpower is provided to form the gas into a plasma. A bias voltage from 0to 100 volts is provided. The Ar gas may be replaced by He, Ne, or Xe.Preferably, the gas is a pure noble gas. In another example, desorptionmay be provided by heating the chuck 308 to a temperature of between 80°C. to 300° C. The process is repeated until the etching of the NVM layer612 is completed. FIG. 6E is a schematic view of the stack 600 after theNVM layer 612 has been etched.

This embodiment uses an IBE to only etch the tunneling layer 616 and toopen the spacer, so that the IBE is used for shallower and lower aspectetching. This allows an IBE that does not form sidewall depositions anddoes not damage the tunneling layer 616. Partially patterning the filmstack puts fewer constraints on the IBE sidewall angle/aspect ratiolimitation while maintaining MgO integrity without deposition build up.The spacer is able to further protect the MgO layer while etchingsubsequent layers. This embodiment uses non-aqueous solvents to avoidpotential degradation of the MgO layer. This embodiment uses vapors tocreate organometallic byproducts, which are volatile in nature and leavethe wafer surface without excessive sidewall buildup. This allows theformation of high density MRAM patterning with high aspect ratio. Thisembodiment provides an anisotropic etch of an MRAM with small CD andhigh aspect ratios. By providing an atomic level etch this embodimentprovides greater control of the etching process.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, modifications, andvarious substitute equivalents, which fall within the scope of thisinvention. It should also be noted that there are many alternative waysof implementing the methods and apparatuses of the present invention. Itis therefore intended that the following appended claims be interpretedas including all such alterations, permutations, and various substituteequivalents as fall within the true spirit and scope of the presentinvention.

What is claimed is:
 1. A method of etching a stack with at least onemetal layer in one or more cycles with each cycle comprising: performingan initiation step, transforming part of the at least one metal layerinto metal oxide, metal halide, or lattice damaged metallic sites; andperforming a reactive step providing one or more cycles, where eachcycle, comprises: providing an organic solvent vapor to form a solvatedmetal, metal halide, or metal oxide state; and providing an organicligand solvent to form volatile organometallic compounds.
 2. The method,as recited in claim 1, wherein the providing an organic solvent vapor toform a solvated metal, metal halide, or metal oxide state and providingan organic ligand solvent to form volatile organometallic compounds areperformed sequentially.
 3. The method, as recited in claim 1, whereinthe providing an organic solvent vapor to form a solvated metal, metalhalide, or metal oxide state and providing an organic ligand solvent toform volatile organometallic compounds are performed simultaneously. 4.The method, as recited in claim 1, wherein the organic solvent vaporcomprises at least one of alcohols, amine, or hydrocarbons.
 5. Themethod, as recited in claim 1, wherein the ligand solvent comprises atleast one of acetylacetonate (acac) family, acetic acid, amides,amidinates, allyls, ethylene, acetylene, and cyclo-pentadienyl.
 6. Amethod of etching a stack with at least one metal layer in one or morecycles with each cycle comprising: performing an initiation step,transforming part of the at least one metal layer into metal oxide,metal halide, or lattice damaged metallic sites; and performing areactive step comprising providing an organic solvent vapor to form asolvated metal, metal halide, or metal oxide state or providing anorganic ligand solvent to form volatile organometallic compounds.
 7. Themethod, as recited in claim 6, further comprising performing adesorption of the volatile organometallic compounds.
 8. The method, asrecited in claim 7, wherein the performing the desorption, comprisesheating the organometallic compounds.
 9. The method, as recited in claim6, wherein the organic solvent vapor comprises at least one of alcohols,amine, or hydrocarbons.
 10. The method, as recited in claim 6, whereinthe ligand solvent comprises at least one of acetylacetonate (acac)family, acetic acid, amides, amidinates, allyls, ethylene, acetylene,and cyclo-pentadienyl.
 11. A method of etching a stack with at least onemetal layer in one or more cycles with each cycle comprising: performingan initiation step, transforming part of the at least one metal layerinto metal oxide, metal halide, or lattice damaged metallic sites; andperforming a reactive step comprising providing an organic solvent vaporto form a solvated metal, metal halide, or metal oxide state.
 12. Themethod, as recited in claim 11, further comprising performing adesorption of volatile organometallic compounds.
 13. The method, asrecited in claim 12, wherein the performing the desorption, comprisesheating the organometallic compounds.
 14. The method, as recited inclaim 11, wherein the organic solvent vapor comprises at least one ofalcohols, amine, or hydrocarbons.
 15. The method, as recited in claim11, further comprising forming a patterned mask, comprising: etching amagnetic tunnel junction layer formed over the stack with an ion beametch or reactive ion etch; forming a spacer layer over the magnetictunnel junction layer; and opening the spacer layer.
 16. A method ofetching a stack with at least one metal layer in one or more cycles witheach cycle comprising: performing an initiation step, transforming partof the at least one metal layer into metal oxide, metal halide, orlattice damaged metallic sites; and performing a reactive step providingan organic ligand solvent to form volatile organometallic compounds. 17.The method, as recited in claim 16, further comprising performing adesorption of the volatile organometallic compounds.
 18. The method, asrecited in claim 17, wherein the performing the desorption, comprisesheating the organometallic compounds.
 19. The method, as recited inclaim 16, wherein the ligand solvent comprises at least one ofacetylacetonate (acac) family, acetic acid, amides, amidinates, allyls,ethylene, acetylene, and cyclo-pentadienyl.
 20. The method, as recitedin claim 16, further comprising forming a patterned mask, comprising:etching a magnetic tunnel junction layer formed over the stack with anion beam etch or reactive ion etch; forming a spacer layer over themagnetic tunnel junction layer; and opening the spacer layer.